Electrical control



W. H. BUDD ETAL ELECTRICAL CONTROL Sept.19,196 7 2 Sheets-Sheet 1 Filed Dec. 9, 1964 FIGURE l v FIGURE '2 INVENTORS WILBERT H. BUDD JOHN AN BENTHUYSEN BY I If A ORNEY Sept. 19, 1967 w. H. BUDD ETAL ELECTRICAL CONTROL 2 Sheets-Sheet 2 Filed Dec. 9, 1964 FIGURE 4 FIGURE 3 FIGURE 5 INVENTORS WILBERT H. BUDD ENTHUYSEN a .N m V T M N H 0 Y JB 6 E R U n, F

United States Patent M 3,343,116 ELECTRICAL CONTROL Wilbert H. Budd, and John D. Van Benthuysen, Elkhart,

Ind., assignors to CTS Corporation, Elkhart, Ind., a corporation of Indiana Filed Dec. 9, 1964, Ser. No. 417,046 16 Claims. (Cl. 338174) ABSTRACT OF THE DISCLOSURE A variable resistance control having a resistance film deposited on an electrically nonconductive U-shaped element. An electrically conductive supporting plate having a collector ring provided with an aperture supports the element with the collector ring disposed in the bight of the U-shaped element. Means integral with the supporting plate restrict movement of the legs of the U-shaped element toward and away from each other. A rotatable member provided with a shaft rotatably journaled in the aperture of the collector ring carries a contactor wipably engaging the resistance film intermediate the ends thereof. An arcuate skirt depending from the rotatable member biases the U-shaped element against the supporting plate. Guide means is also preferably provided on the rotatable member for directing a tool into engagement with a slot provided in the rotatable member.

The present invention relates to electrical controls, and, more particularly, to a variable resistance control of the type provided with a movable contactor.

One type of variable resistance control provided with a movable contactor employs a carbon film for the resistance path. The carbon film is usually deposited on a surface of an elongated thin strip of electrically nonconductive element material and a U-shaped resistance element is punched out of the material. The resistance element is fixedly mounted by suitable means, e.g., rivets, to an electrically nonconductive base of the control. By fixedly mounting the resistance element to the base, twisting or separation of the legs of the U-shaped resistance element is prevented when the control is assembled, mounted and operated. During the past years, many changes have been made to this type of variable resistance control to decrease the cost of manufacture thereof. In an effort to decrease the cost of manufacture and the number of parts of a variable resistance control, the resistance material has been embedded or molded into the base. The molded element controls are, however, limited to certain applications. It

would, therefore, be desirable to reduce the number of parts of a variable resistance control as well as decrease the cost thereof by eliminating the base of the control and securing the parts of the control directly to the U-shaped resistance element.

To facilitate adjustment, most electronic equipment such as television sets was initially designed by providing the variable resistance controls near the access panels in order that the shafts of the controls would extend through openings in the access panels. Recently, more emphasis has been placed on cost reduction, and consequently, economy dictates the location of many variable resistance controls in electronic equipment. Additional means must, therefore, be employed for adjusting or operating a control when the control is remotely located from the access panel and when it is uneconomical to extend the shaft of the control through the access panel. These conditions usually occur when the control is infrequently adjusted. Such a control is commonly referred to as a preset control, i.e., a control which is adjusted during assembly of the equipment and thereafter only when the equipment is repaired. Special tools, such as a screwdriver having an Patented Sept. 19, 1967 elongated electrically nonconductive shaft, are employed for adjusting the preset controls. Difficulties, however, are encountered in inserting the end of thetool into a slot or suitable configuration provided in the rotatable member of the control when the preset control is remotely located from the access panel. It would, therefore, also be desirable to provide a variable resistance control with means for facilitating the engagement of a tool with a control for adjusting the same.

Accordingly, it is an object of the present invention to provide a new and improved variable resistance control having the various desirable features set forth above.

Another object of the present invention is to provide a variable resistance control having a U-shaped resistance element with means for restricting the inward and outward movement of the legs of the U-shaped resistance element with respect to each other.

An additional object of the present invention is to provide a variable resistance control with a rotatable member having an arcuate skirt portion slideably engaging the inner edge of the resistance film on the U-shaped resistance element.

A further object of the present invention is to provide a variable resistance control employing a rotatable member substantially larger in diameter than the diameter of the arcuate portion of the U-shaped resistance element.

Still another object of the present invention is to provide a variable resistance control with means for biasing the U-shaped resistance element against a supporting plate of the control for maintaining the resistance element in a single plane.

Still an additional object of the present invention is to provide a variable resistance control with a disc type rotatable member in order that an arcuate portion thereof can be inserted through a slot in an access panel for facilitating adjustment of the control.

A still further object of the present invention is to provide a variable resistance control employing a rotatable member having a centrally disposed slot and guide means for directing a tool into engagement with the slot when the control is remotely located from an access panel.

Yet another object of the present invention is to provide a variable resistance control employing a rotatable member having a centrally disposed slot communicating with an opening in a hollow shaft integral with the member in order that the end of a tool used for adjusting the control does not impinge against the bottom of the slot when inserted thereinto.

Yet a further object of the present invention is to provide a variable resistance control with a high diameter to thickness ratio.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, the present invention is concerned with a variable resistance control comprising an electrically nonconductive U-shaped element material having a resistance film deposited on a surface thereof to define a U-shaped resistance element. A supporting plate having a collector ring provided with an aperture carries the U-shaped resistance element with the collector ring being concentric with the opening of the resistance element. The supporting plate is provided with means restricting movement of the legs of the U-shaped resistance element toward each other while additional means associated with the supporting plate restrict movement of the legs away from the collector ring. A rotatable member provided with a shaft rotatably journaled in the aperture of the collector ring carries a contactor for wiping the resistance film intermediate the ends thereof. The shaft in one embodiment is hollow and communicates with a slot in the rotatable member. The end of the shaft projecting through the aperture in the collector ring is swaged for rotatably securing the rotatable member to the supporting plate. The rotatable member is also provided with a depending arcuate skirt for biasing the U-shaped resistance element against the supporting plate. In another embodiment of the present invention, guide means is provided on the rotatable member for directing a tool into engagement with a slot provided in the rotatable member.

For a better understanding of the present invention, reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein:

FIGURE 1 is an isometric rear View of an improved variable resistance control built in accord with the present invention;

FIGURE 2 is a sectional view of the control shown in FIGURE 1, the control being mounted adjacent to an access panel;

FIGURE 3 is an exploded view of the variable resistance control shown in FIGURE 1;

FIGURE 4 is a front view of the control of FIGURE 1 with a portion of the knob removed;

FIGURE 5 is a side view of an additional embodiment of a variable resistance control of the present invention, the control being remotely mounted from an access panel; and

FIGURE 6 is a front plan view of the control shown in FIGURE 5.

Referring now to the drawings, there is illustrated a variable resistance control, generally} indicated at 10 comprising a supporting plate 11, a U-shaped resistance element 20, a rotatable member 30, and an equalizing contactor 40 engaging the resistance element 20 and constrained to rotate with the rotatable member 30.

Considering first the supporting plate 11, it preferably comprises a one-piece sheet metal stamping of circular configuration with a segment removed. A collector .ring 12 embossed from the flat center portion 13 of the supporting plate 11 extends outwardly thereof, as best seen in FIGURES 2 and 3 of the drawings, the outer periphery or upstanding portion 12a of the collector ring being positioned adjacent to the edge of an opening or bight portion 21 of the U-shaped resistance element 20 for aligning the resistance element with the collector ring 12. The distance the outer periphery 12a of the collector ring 12 projects into the opening 21 is critical, since, as described in more detail hereinafter, the collector ring 12 must be spaced from the top of the resistance element 20 so as to be insulated therefrom.

The resistance element 20 is punched from an electrically nonconductive element material such as laminated plastic. The thickness of the element material should be sufficient to avoid flexing of the legs after the resistance element 20 is biased against the supporting plate 11. It is also advantageous to have the thickness of the element material as thick as possible since this improves the heat dissipating qualities of the resistance element and consequently permits the control 10 to be rated at a higher wattage rating. Element material thickness of .040 inch are, therefore, preferred to a .020 inch material. Initially a not-shown elongated strip of electrically nonconductive element material is coated in a manner well known in the art with a resistance film comprising a carrier containing carbon particles or other suitable material and with a conductive film in overlapping relationship with the resistance film. The elongated strip is then fed into a die mounted in a punch press for punching the resistance element 20 of U-shaped construction from the strip of element material. The U-shaped construction is generally preferred since such configuration assure that the conductive lands 23a and 23b on the legs 20a and 20b of the U-shaped resistance element 20 are properly spaced from each other.

Otherwise, if the legs were not spaced from each other, it would be necessary to provide another step for removing the conductive film 23 bridging the conductive lands 23a and 23b. As best shown in FIGURE 4 of the drawings, the resistance film 22 is defined by an arcuate portion 221;: of the U-shaped resistance element 20, and the conductive film 23 is defined by the conductive lands 23a and 23b disposed in overlapping relationship with the ends of the resistance film 22.

It, therefore, becomes apparent that the outer periphery 12a of the collector ring 12 engage only the lower edge of the opening 21 for centering the collector ring 12 in the opening 21 and that the upper edge of the opening 21 be properly spaced from the collector ring 12 so as to avoid making contact with the inner edge of the resistance film 22 adjacent to the upper edge of the opening. If the collector ring is not embossed, then other means such as ears can engage the lower edge of the opening 21. A sufiicient gap is provided between the upper edge of the opening 21, more specifically, the inner edge of the resistance film 22, and the collector ring by forming :a bevel 12b between the outer periphery 12a and the top surface of the collector ring 12. The gap must be sufiicient to withstand the ground test voltage the control 10 is subjected to after assembly.

A pair of terminals 25a and 25b are secured to the legs of the U-shaped resistance element 20 for connecting the arcuate resistance film 20 into an electrical circuit. The legs of the U-shaped resistance element are provided with inwardly extending st-ub portions 20c and 20d, the ends of which define a slot 24 therebetween. Each of the terminals 25a and 25b is provided with three clinching ears. Two of the clinching ears are opposite each other and are folded over each of the inwardly extending stub portions 200 and 20d. The third clinching ear of each terminal is disposed at a right angle to the other two ears and is folded over the outer edge of the leg for fixedly securing the terminal to the U-shaped resistance element 20.

To prevent relative rotation between the U-shaped resistance element 20 and the supporting plate 11, a pair of upended ears 14 are disposed along the periphery of the fiat center portion 13 of the supporting plate 11 adjacent to the chordal line 14 defining the removed segment of the supporting plate 11 and engage suitable notches 26 in the resistance element 20. In a preferred form of the invention, the ears 14 not only prevent relative rotation between the resistance element 20 and the supporting plate 11 but also function as stop ears for restricting outward movement of the legs of the U-shaped base with respect to each other. A terminal 15 integral with the supporting plate 11 and extending normal from the periphery of the fiat center portion 13 connects the collector ring 12 into the electrical circuit.

Inasmuch as the legs 20a and 20b are spaced from each other, it is desirable that means be employed for biasing the resistance element against the supporting plate 11 with sufficient force to prevent twisting or inadvertent movement of the legs of the resistance element during mounting and adjusting of the control 10. To this end, the rotatable member 30 is provided with a depending arcuate skirt 31 engaging the inner edge of the resistance film 22 of the U-shaped resistance element 20 adjacent to the opening 21. The rotatable member 30 is provided with a stub shaft 32 rotatably secured to the supporting plate 11 for biasing the outer edge of the skirt 31 against the inner edge of the resistance film thereby urging the U- shaped resistance element 20 against the flat center portion 13 of the supporting plate 11.

According to the present invention, the rotatable member 30 preferably is molded of an electrically nonconductive heat-deformable material such as nylon. The stub shaft 32 extending inwardly of and integral with the rotatable member 30 is journaled in an aperture 12d provided in the collector ring 12. The parts of the variable resistance control 10, therefore, can be readily assembled together by merely inserting the end of the stub shaft 32 into the aperture 120! of the collector ring 12 and heat swaging the end of the shaft 32 projecting outwardly from the collector ring 12 as shown in FIG- URES 1 and 2 of the drawings. Since the collector ring 12 is coaxially mounted with the arcuate portion of the resistance element 20, the rotatable member 30 is also in axial alignment with the resistance film 22 forming a part of the element 20. A not-shown heated cylindrical tool of suitable construction is employed for swaging the end of the shaft 32 against the collector ring. During the swaging operation, the diameter of the shaft disposed in the aperture 12d of the collector ring 12 is increased slightly thereby assuring a tight bearing fit between the shaft 32 and the bearing or aperture 12d.

When the control is employed in a circuit requiring frequent adjustment, the edge of the collector ring defining the aperture 12d is increased by forming a cylindrical flange 12e at the edge to increase the peripheral area of the bearing. By forcing the rotatable member 30 against the supporting plate 11 during the swaging operation, the skirt 31 integral with the rotatable member 30 biases the U-shaped resistance element 20 against the flat center portion 13 of the supporting plate 11 thereby constraining the resistance element to remain in a plane parallel to the major surface of the flat center portion 13.

The contact-or 40 is carried by the rotatable member 30, and to constrain the contactor 40 to rotate with the rotatable member 30, the skirt 31 is provided with a pair of diametrically opposed notches 33, as seen in FIG- URE 3 of the drawings, and a pair of outwardly extending diametrically opposed arms 41 integrally connected to the contactor 40 are disposed within the notches 33. The contactor 40 also provided with a pair of contacts 42 and 43, is nestedly received in an annular cavity 34 defined by the outer edge of the shaft 32 and the inner edge of the skirt 31. The contact 42 is disposed in a slot 35 and extends a greater distance from the axis of the shaft 32 than the contact 43 of the contactor 40 making electrical engagement with the arcuate resistance film 22. Contact 43 engages the top surface 120 of the collector ring 12. The arms 41 of the contactor are preformed to have a V cross section which forms a crease extending through both arms as shown in FIGURE 3 of the drawings. The crease stiffens the contactor 40 and the bottom edge of the V forms pivot edges 44a for enabling pivotal movement of the contactor 40. Therefore, any difference in contact pressure caused by manufacturing tolerances resulting from forming the contactor and any variation in the dimension between the top surface 12c of the collector ring and the arcuate resistance film 22 is compensated since the contactor 40 merely pivots on edges 44a and balances the contact pressures in a preset ratio.

From the above description, it is apparent that the variable resistance control can be rapidly assembled in production. For example, the rotatable member 30 is carried by a movable supporting surface and the contactor 40 is automatically assembled to the rotatable member 30 by merely dropping the contactor over the shaft 32 with the arms 41 and the contact 42 of the contactor in alignment with the slots 33 and 35 respectively. The resistance element 20 having the arcuate resistance film 22 and the conductive lands in overlapping relationship with the ends of the arcuate resistance film bonded to a surface thereof and a terminal fixedly secured to each of the conductive lands 23a and 23b is assembled to the supporting plate 11. After the supporting plate 11 and the resistance element 20 are assembled together and dropped over the shaft 32 projecting from the rotatable member 30, it is merely necessary to compress the parts together and heat swage the end of the partially hollow stub shaft 32 to secure the supporting plate to the rotatable member 30. The force with which the supporting plate 11 is pressed against the rotatable member 30 determines the ultimate rotational torque between the rotatable member 30 and the resistance element 20. Thus a change in the rotational torque of the variable resistance control may be obtained by merely altering the force compressing the parts together. A stop also depends from the rotatable member and is engageable with the legs for limiting angular rotation of the contactor. When it is preferable to limit the angular rotation of the contactor 40 to less than the angle spanned by the legs, a stop member 16 is provided on the supporting plate as seen in FIGURE 4 of the drawings. The stop member is integral with the supporting plate and can be located at any angle on the periphery thereof. The rotatable member is provided with a depending peripheral rim 36 for increasing the structural strength thereof, and a plurality of undulations 37 is provided on the peripheral rim of the rotatable member to facilitate manual rotation thereof without a suitable tool.

In order that the variable resistance control 10 can be quickly adjusted with a tool such as a screwdriver, slots 32b and 35 are provided in the cavity of the shaft 32 and on the front surface of the rotatable member respectively. It will be appreciated that an arrow cooperating with the slot may be provided on the front face of the rotatable member 30 to indicate the angular position of the contactor.

In another embodiment, when a control 110 is positioned toward the center of the chassis, i.e., remotely located from an access panel 150, a cone 136 (see FIGURE 5 is integrally molded with the rotatable member 130 for guiding the end of the tool into the slot 135. Suitable guiding slots 137 are provided in the cone 136 for facilitating insertion of the end of the tool in the slot whenever the end of the tool is initially 90 out of phase with the slot. A hollow shaft 132 is integrally secured to the rotatable member 130 and the opening in the shaft communicates with the slot. Thus a tool with tapered sides can be inserted into the slot without having the end of the tool engage the bottom of the slot.

While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention, and additional modifications thereof, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a variable resistance control, the combination of an electrically conductive supporting plate, a U-shaped element having a pair of spaced legs mounted on the supporting plate, a resistance film bonded onto a surface of the U-shaped element, a collector ring integral with the supporting plate, means integral With the supporting plate restricting inward and outward movement of the legs with respect to each other, a contactor in wiping contact with the resistance film and the collector ring, rotatable means constraining the contactor to rotate therewith, and biasing means maintaining the U-shaped element in a plane parallel to the supporting plate.

27 In a variable resistance control, the combination of an electrically conductive supporting plate, a collector ring integral with the supporting plate, a U-shaped element having a pair of spaced legs mounted on the supporting plate, a resistance film bonded onto a surface of the U-shaped element, means integral with the supporting plate restricting inward and outward movement of the legs with respect to each other, means maintaining the U-shaped element in a plane parallel to the supporting plate, and a contactor adapted to wipe the resistance film and the collector ring.

3. The variable resistance control of claim 2 wherein a stop is carried by the supporting plate for restricting angular rotation of the contactor.

4. In a variable resistance control, the combination of an electrically conductive supporting plate, a U-shaped element having a bight portion and disposed on the supporting plate, a resistance film bonded onto a surface of the U-shaped element, a terminal connected to one end of the resistance film, a collector ring embossed from the plane of the supporting plate and projecting in the bight portion of the U-shaped element restricting movement of the legs toward each other, means maintaining the U- shaped element in a plane parallel to the supporting plate, and a contactor adapted to wipe the resistance film and the collector ring.

5. In a variable resistance control, the combination of an electrically conductive supporting plate, an apertured element disposed on the supporting plate, first means defining an arcuate resistance path having a pair of ends, the first means being bonded to the element and extending around the aperture, second means defining a conductive path in overlapping relationship with a portion of the first means, a terminal connected to the second means, third means insulatedly spacing the ends of the resistance path from each other, fourth means slideably engaging the first means and maintaining the first means flatwise in a plane relative to the supporting plate, and fifth means for making wiping contact with the first means intermediate the ends thereof.

6. In a variable resistance control, the combination of an electrically conductive supporting plate, a split ring element disposed on the supporting plate and having a pair of spaced end portions defining a slot, first means defining an arcuate resistance path carried by the split ring element, second means defining a conductive path in overlapping relationship with a portion of the first means adjacent to the slot splitting the element, a terminal connected to the conductive path, third means maintaining the first means flatwise in a plane relative to the supporting plate, fourth means integral with the supporting plate restricting inward and outward movement of the end portions of the split ring element with respect to each other, and fifth means for making wiping contact with the first means intermediate the ends thereof.

7. The variable resistance control of claim 6 wherein the third means comprises a rotatable member and an arcuate skirt integral with the rotatable member biases the element and the first means carried by the element against the supporting plate, and a shaft integral with the rotatable member is provided with a bore communicating with a slot provided in the rotatable member.

8. A variable resistance control comprising a resistance element having a resistance film provided with a pair of ends bonded onto a surface thereof, said resistance element being provided with an opening, a conductive land bonded to the ends of the resistance film, an apertured electrically conductive supporting plate carrying the resistance element, the center portion of the supporting plate defining a collector ring disposed in the opening, means insulatedly spacing the ends of the resistance element, a rotatable member, a shaft of heat-deformable material integral with the rotatable member and rotatably journaled in the aperture provided in the supporting plate, a skirt integral with the rotatable member having an edge slideably engaging the resistance film, the end of the shaft being enlarged to maintain the' supporting plateand the resistance element in fixed relationship with the rotating member, and a contactor carried by the rotatable member in wiping contact with the resistance element intermediate the ends thereof.

9. In a variable resistance control, the combination of an electrically conductive supporting plate, a split ring element disposed on the supporting plate and having a pair of spaced end portions, first means centering the element on the supporting plate, second means defining an arcuate resistance path carried by the split ring element, third means defining a conductive path in overlapping relationship with a portion of the second means defining the arcuate resistance path, the supporting plate being provided with a centrally disposed aperture, a rotatable member, a shaft integral with the rotatable member and journaled in the aperture rotatably supporting the rotatable member with respect to the supporting plate and the split ring element, fourth means integral with the IQ- tatable member biasing the split ring element flatwise in a plane against the supporting plate, fifth means for making wiping contact with the second means intermediate the end thereof, and sixth means integral with the supporting plate fixedly spacing the end portions of the split ring element material with respect to each other.

10. The variable resistance control of claim 9 comprising means integral with the rotatable member for facilitating rotation thereof when the control is remotely mounted from an access panel.

11. A variable resistance control comprising an electrically conductive supporting plate, a U-shaped element having a pair of spaced legs and mounted on the supporting plate, a resistance film bonded onto a surface of the U-shaped element, a conductive land bonded onto each of the legs in overlapping relationship with the resistance film, a terminal electrically connected to each of the conductive lands, a collector ring embossed from the plane of the supporting plate having a top surface and a peripheral edge, the peripheral edge engaging the bight of the U-shapedelement and restricting movement of the legs toward each other, the top surface of the collector ring being spaced from the surface of the U-shaped element and the resistance film, the top surface of the collector ring being provided with an aperture, a rotatable member, a shaft connected to the rotatable member and rotatably journaled in the aperture, an arcuate skirt depending from the rotatable member slideably engaging the inner edge of the resistance film and maintaining the U-shaped element in a plane parallel to the supporting plate, and a contactor adapted to wipe the resistance film and the col lector ring.

12. A variable resistance control comprising an arcuate resistance element having a resistance film bonded onto a surface thereof, said resistance element being provided with an opening and a pair of spaced ends, a conductive land bonded onto each of the ends of the resistance element in overlapping relationship with the resistance film, an apertured electrically conductive supporting plate carrying the arcuate resistance element, the center portion of the supporting plate defining a collector ring disposed in the opening, means carried by the supporting plate restricting inward and outward movement of the ends of the resistance element with respect to each other, a rotatable member, a hollow shaft of heat-deformable material integral with the rotatable member and rotatably journaled in the aperture provided in the supporting plate, the rotatable member being provided with a centrally disposed slot and the bore in the shaft communicating with the slot, the end of the shaft being swaged to maintain the supporting plate in fixed relationship with the rotating member, and a contactor carried by the rotatable member in Wiping contact with the arcuate resistance element intermediate the ends thereof.

13. A variable resistance control of claim 12 wherein a cone projects outwardly from one side of the rotatable member for facilitating insertion of a tool into the slot provided in the rotatable member.

14. A variable resistance control comprising an arcuate element provided with an opening and a pair of spaced ends, an arcuate resistance film bonded onto the arcuate element, a conductive land bonded onto each of the ends of the element in overlapping relationship with the resistance film, an apertured electrically conductive supporting plate carrying the arcuate element, a collector ring embossed from the supporting plate projecting into the opening, a pair of stop ears integral with the supporting plate, the stop ears engaging the outer edges of the spaced ends of the arcuate element and restricting outward movement of the spaced ends with respect to each other, a rotatable member, an arcuate skirt depending from the rotatable member slideably engaging the inner edge of the arcuate resistance film, a shaft of heat-deformable material connected to the rotatable member and rotatably journaled in the'aperture provided in the supporting plate, the end of the shaft being swaged to maintain the supporting plate in assembled relationship with the rotatable member, and a contactor carried by the rotatable member for wiping the arcuate resistance film intermediate the ends thereof.

15. In a variable resistance control, the combination of an electrically nonconductive U-shaped element, a resistance film bonded onto a surface of the U-shaped element, a rotatable member mounted adjacent to the resistance film, means constrained to rotate with the rotatable member for making wiping contact with the resistance film intermediate the ends thereof, the rotatable member being provided with a slot, and means provided in the rotatable member and projecting forwardly of the slot facilitating the insertion of a tool into the slot when the 20 control is remotely mounted from an access panel.

16. In a variable resistance control, the combination of an electrically conductive supporting plate, a U-shaped element having a pair of spaced legs mounted on the supporting plate, a resistance film bonded onto a surface of the element, a rotatable member mounted adjacent to the resistance film, means constrained to rotate with the rotatable member for making wiping contact with the resistance film intermediate the ends thereof, the rotatable References Cited UNITED STATES PATENTS 2,443,018 6/1948 Arvin et 'al. 338 174 2,745,927 5/1956 Daily etal 338--174X 2,946,032 7/1960 Daily 338--174 3,119,089 1/1964 Murry 338-174 FOREIGN PATENTS 948,297 1/1964 Great Britain.

RICHARD M. WOOD, Primary Examiner.

J. G. SMITH, Assistant Examiner. 

1. IN A VARIABLE RESISTANCE CONTROL, THE COMBINATION OF AN ELECTRICALLY CONDUCTIVE SUPPORTING PLATE, A U-SHAPED ELEMENT HAVING A PAIR OF SPACED LEGS MOUNTED ON THE SUPPORTING PLATE, A RESISTANCE FILM BONDED ONTO A SURFACE OF THE U-SHAPED ELEMENT, A COLLECTOR INTEGRAL WITH THE SUPPORTING PLATE, MEANS INTEGRAL WITH THE SUPPORTING PLATE RESTRICTING INWARD AND OUTWARD MOVEMENT OF THE LEGS WITH 